ok a/f sensors by the looks of it is a 02 sensor and we know 02 sensors are heated sounds like some kind of 02 sensor code. usually ill clear the code if it comes back replace it
when you replace it on some vehicles it takes about 10 minutes for the ecu to recognize it has been changed and the code becomes inactive.also sometimes you must reset the fuel table parameters dont think this applies to you though .

P0135 if a heater code for the heating element inside the O2 sensor. The heating element quickly heats up the O2 sensor so that it begins to properly read faster. (A cold O2 sensor is inaccurate) The P0135 code typically means that you will need to replace the sensor itself. However you do want to check the heater control circuit first to be sure there is not a power/control problem.

My CEL light came on as well. My truck suddenly had lots of power but the gas mileage went to crap. I ran a scan and the P1135 code (and only this code) came up. Fuel/Air sensor 1 bank 1. I'll order the Denso part but wanted to make sure that I pull the right sensor. Bank 1 Sensor 1 is the sensor accessible from behind the right front tire, correct? I know that it is also accessible from underneath as well but for description sake.